The present invention relates to scaffold fixation devices useful in articular cartilage repair and more specifically to a device for fastening an articular cartilage scaffold to underlying bone.
Articular cartilage is a tissue that covers the articulating surfaces between bones in joints, such as the knee or elbow, which is subject to catastrophic or repetitive stress injury. Various means have been proposed to address such injuries including repair via tissue engineering. Tissue engineering is defined as the application of engineering disciplines to either maintain existing tissue structures or to enable new tissue growth. This engineering approach generally includes the delivery of a tissue scaffold that serves as an architectural support onto which cells may attach, proliferate, and synthesize new tissue to repair a wound or defect. Surgical use of a tissue scaffold requires a fixation means to secure the scaffold to the bone beneath the wounded cartilage site. Secure fixation of the scaffold within the wound site is necessary for proper healing.
Frequently, scaffolds, prostheses and fasteners used in orthopedic applications are made from synthetic absorbable biocompatible polymers which are well known in the art. Such polymers typically are used to manufacture medical devices which are implanted in body tissue and absorb over time. Synthetic, absorbable, biocompatible aliphatic polyesters include homopolymers, copolymers (random, block, segmented and graft) of monomers such as glycolic acid, glycolide, lactic acid, lactide(d, I, meso and mixtures thereof), xcex5-caprolactone, trimethylene carbonate and p-dioxanone. Numerous U.S. Patents describe these polymers, including U.S. Pat. Nos. 5,431,679; 5,403,347; 5,314,989; and 5,502,159. Devices made of an absorbable material have the advantage that they are absorbed by the body after healing has occurred.
U.S. Pat. No. 5,067,964 describes an articular cartilage repair piece which includes a backing layer of non-woven, feted fibrous material which is either uncoated or covered by a coating of tough, pliable material. A number of means are disclosed for fastening the repair piece to the underlying bone. U.S. Pat. Nos. 5,306,311 and 5,624,463 describe a prosthetic, resorbable articular cartilage and methods of its fabrication and insertion. U.S. Pat. No. 5,713,374 describes an attachment method to hold a biomaterial in place until healing occurs. U.S. Pat. Nos. 5,632,745 and 5,749,874 and 5,769,899 describe a bioabsorbable cartilage repair system.
Articular joint loading is very complex, involving high compressive loads combined with high shear loads associated with sliding articulation of the opposing surfaces. A device implanted into the articular joint space must have sufficient strength to withstand these loads. Particularly important is that the device should be fixed in the underlying bone so that it cannot rotate or separate from the bone under the action of high shear loads in the joint space. U.S. Pat. No. 5,749,874 teaches that if vascular invasion and cellular migration is to be effected between the healthy tissue and the scaffold, means must be provided to preclude rotation of the scaffold relative to the fixation device, but does not describe a means of keeping the fixation device itself from rotating in relation to the surrounding tissues or from pulling out.
Accordingly, it would be advantageous to provide a scaffold fixation device which has a fixation means that engages the bone to prevent rotation and separation.
The limitations of prior art devices for attaching a tissue scaffold to bone tissue are overcome by the present invention which includes an attachment device having a platform positionable in substantially parallel relationship to the bone tissue for retaining the tissue scaffold proximate to the bone tissue. A post extends from the platform and is insertable into a hole formed in the bone tissue. At least one rib extends from a surface of the post along a portion of its length from a first point distal to the platform to a second point intermediate the first point and the platform. The rib has a cross-sectional area that increases along the length of the rib in the direction from the first point to the second point and establishes an interference fit relative to the hole in the bone tissue to prevent rotation of the device relative to the bone tissue.